Provider Backbone Bridge Traffic Engineering (“PBB-TE”) uses an end-to-end 1:1 protection paradigm, referred to in this document as “e2e protection”. This provides a robust protection mechanism which can be used across an arbitrary mesh of network connectivity. However, the underlying physical connectivity of many networks frequently uses rings of fiber, which makes protection over ring topologies an important scenario. In a network of cascaded rings as illustrated in FIG. 1, matched pairs of nodes are used to interconnect communication links of logically adjacent rings. A primary path between endpoints traverses links between ones of the matched pairs of nodes, i.e., primary path nodes. A protection path traverses different links between the corresponding nodes of the matched pairs of nodes, i.e., protection path nodes. Each path in PBB-TE is associated with a VLAN ID (VID). In the event of a fault in a link or node of the primary path, traffic is switched to the protection path by the headend endpoint changing the VID used on data frames.
Although the end-to-end 1:1 protection paradigm works well, it has some drawbacks. For example, different rings may be associated with different geographic domains that are managed and operated by different organizations within the carrier, and each organization may wish to schedule maintenance outages without coordinating with other organizations. Further, in long distance communication deployments, the frequency of faults on the extended e2e path can become significant enough that probability of a second fault occurring on the protection path before a first fault is repaired becomes unacceptable. An extended e2e protection paradigm can be used to mitigate this, but the number of required protection paths grows significantly as a function of the number of rings and extent of protection, e.g., protection from multiple faults across multiple rings. For example, four end-to-end paths are required for decoupling of a pair of rings in cascade since there are four possible paths. In the case of three rings in cascade, six paths are required for protection against two independent faults on any pair of rings, and eight paths are required for full protection against a single simultaneous fault on each ring. Maintaining a large number of paths can be problematic because forwarding state is directly related to the number of paths installed, and every path adds a Connectivity Fault Management (“CFM”) session to the terminating nodes.